1. Alpha-amylase
Alpha-amylase [.alpha.(1.fwdarw.4)-glucan 4-glucanohydrolase]is an enzyme which participates in the digestion of starch in the human gastrointestinal tract. The enzyme is produced in the pancreas and parotid glands of humans where it is secreted into pancreatic juice and saliva, respectively. The .alpha.-amylase enzyme can also be found in low but measurable quantities in body fluids such as blood serum and urine.
The concentration of .alpha.-amylase in a patient's test sample, such as a serum or urine sample, may exhibit changes which are of clinical significance. Changes in test sample .alpha.-amylase concentration can be observed due to a variety of pathological conditions. For example, the test sample taken from a patient afflicted with pancreatitis, mumps or pancreatic cancer will generally show a much higher level of .alpha.-amylase than a test sample from a healthy donor. Liver diseases, on the other hand, will generally cause lower .alpha.-amylase levels than would be observed in a healthy individual.
Starches form the basic molecular storage reservoirs for plants. As such, they also provide a common energy source in the human diet. The .alpha.-amylase produced in humans participates in the digestion of this starch. All starches are homogenous, containing only D-glucose residues. Rather than single molecules, these starches are normally mixtures of two structurally distinct polysaccharides. One component is termed amylose, the other amylopectin. Both are poly-.alpha.-D-glucose molecules. Amylose is a linear molecule with all glucose residues linked via .alpha.(1.fwdarw.4) bonds. Amylopectin, on the other hand, is a branched molecule due to the presence of a small number of .alpha.(1.fwdarw.6) linkages at various points along a core chain consisting of .alpha.(1.fwdarw.4) linkages.
Both .alpha.-amylase and .alpha.-amylase (produced in plants) attack the amylose and amylopectin fractions of starch at .alpha.(1.fwdarw.4) sites but in a different pattern. Cleavage with .alpha.-amylase is random, occurring at different loci to yield a mixture of glucose and maltose; maltose being a disacharride consisting of two D-glucose residues connected through an .alpha.(1.fwdarw.4) linkage. The action of .beta.-amylase is more ordered, characterized by successive removal of only maltose units, beginning at a non-reducing terminus. See FIG. 1. Neither enzyme is capable of hydrolyzing the .alpha.(1.fwdarw.6) linkages. Thus, whereas the combined action of the two enzymes will completely degrade amylose to glucose and maltose, amylopectin is only partially degraded However, other catalysts, called debranching enzymes, specific for hydrolyzing the .alpha.(1.fwdarw.6) linkage, do exist in nature.